The need for power protection is not new. It has long been known that even simple fluctuations of electrical line voltage can have disastrous results on attached electrical equipment. It is known that an electrical light bulb can fail if the operating voltage exceeds the prescribed limits. For example, a ten percent increase in line voltage can reduce the filament life of a common light bulb by half. Increasing the AC line voltage from 120 volts to 144 volts can reduce the design life of an electric bulb from 750 hours to less than 200 hours. Voltage sags and surges, are but one of the problems that must be eliminated. Other serious defects include, but are not limited to voltage spikes and transients, glitches, dropouts (prolonged glitches), and electrical noise. An interesting case which illustrates these problems is reported to have occurred at General Motors. A computer controlled vehicle painting system was in operation, painting a new car Blue. Suddenly, about halfway through the process, the paint color changed ro Red. An investigation revealed that a welder on the same power line was causing transients on the power line. These transients affected the attached painting computer and caused it to switch colors out of sequence.
Early Power Protection Devices
In order to solve the problem of line voltage surges and sags, Sola invented the constant voltage transformer in 1938 (U.S. Pat. No. 2,136,895). This magnetic device could reduce voltage fluctuations of plus and minus twenty percent to a low value of plus and minus two percent, resulting in immediate industrial savings of hundreds of thousands of dollars by simply extending the operating life of light bulbs which were in use as street and industrial lighting. As science progressed, heavy current consuming devices were added to the power lines, and the quality of electrical power became worse Elevators and heavy lighting loads caused the power lines to fluctuate badly. Connection of inductive loads such as motors and electromagnets caused the electrical power mains to develop transients of several thousands of volts when these loads were turned on and off. Power distribution management by electrical provider companies has necessitated the installation of relays which transfer power from one power distribution grid to another.
As these relays transfer power, there is an interruption or break of power whose duration can be from a fraction of a cycle to several cycles. (one cycle of a 60 cycle AC voltage source is equal to 16.6 milliseconds). Welders or other electrical equipments on the AC line can cause severe electrical noise to occur, and the effects of lightning are often extremely severe. A lightning strike which occurs twenty miles away from a factory or home can induce electrical transients on the power line which are sufficient to damage or destroy electrical equipment. A nearby lightning strike can induce voltages in the order of 8,000 volts and thousands of amperes in the electrical power system of a home or factory.
Recent Developments
In recent years, the power quality has become aggravated by the increased use of computers, television sets, VCR's, and other extremely sensitive electronic equipment. Many of these equipments are used in industry, in medical applications, and in the home. A new industry has evolved specifically to provide reliable and efficient methods of power protection. Standards have been established which define the allowable disturbances that can exist on the power lines. Some classes of modern electronic equipment have been modified to withstand a specific level of power disturbance without erratic operation. This requirement, promulgated by by the Computer Business Equipment Manufacturers Association, is known as the CBEMA curve.
The most prevalent type of power protection device in use today is the Uninterruptible Power Supply (UPS). The line fault detection systems are relatively simple, these devices respond to failures on the power mains, and almost immediately transfer to battery backup wherein a battery powers an inverter which creates an artificial AC voltage (often square waves) to provide power to the attached equipment. These UPS products often operate unnecessarily, depleting the batteries when the line defect is small. In addition, many line defects are of such short duration, that the use of an inverter is not necessary.
It is an object of the present invention to correct these difficulties by providing a control system which does not react to small line voltage abnormalities, but rather, accumulates the data over a specified time, analyzes the trend of the line changes, and then predicts the probability or imminence of power line failures.
Supplementary Information Relevant to the Present Invention
The constant voltage transformer which was developed by Mr. Sola, although simple and functional, was very primitive. Input energy, measured as volt-amperes was fairly constant over most of the load range. This meant that when a small load was connected to the Sola Constant Voltage Transformer, the transformer consumed almost as many volt-amperes, with a power factor approaching unity, as when the full rated load was connected. This represented an inefficiency which was costly to the user, and which caused the transformer to overheat.
Modem Ferroresonant transformer technology, spearheaded by such companies as Best Power Technology, in the 1980's and 1990's, have improved the original Sola design, and have created a new breed of constant voltage transformers which are more efficient, and whose input power was proportional to the load volt-amperes. These new types of Ferroresonant transformers provide isolation and excellent protection against the effects of lightning transients, glitches, noise, and fluctuating line voltage.
These specialized magnetic devices could provide excellent voltage regulation, and they could accept a lightning strike of more than 8000 volts without damage, and then reduce the voltage surge which reaches the sensitive equipment attached thereto, to three volts or less.
The Ferrorersonant transformer has formed the basis for a nearly ideal, but simple, power conditioner, manufactured by Best Power technology, Necedah Wisconsin, under the trade names of FERRUPS and CITADEL.
In addition to its phenomenal isolation properties, the Ferroresonant transformer also has the ability to store electrical energy and provide power to the connected load during a short power outage, keeping the load fully powered during the momentary disruption of power.
These bursts of energy which can be supplied by the Ferroresonant transformer can be as long as twenty milliseconds under full load conditions, in the event of a complete power failure. Power line dropouts caused by relay transfer, usually in the ten to fifteen millisecond range, will not pass through the Ferroresonant based power conditioner. The magnetic energy which is stored in the "tank circuit" will power the output during the relay transfers, or power breaks, keeping the flow of power to the critical load smooth, continuous, and sinusoidal.
Prior art UPS products, and in particular, Ferroresonant based UPS products examine the incoming line for defects, and when predefined defects occur, the inverter system is automatically turned on, thus providing a measure of power protection which is automatic.
A major defect in the present UPS art is that the incoming power line must absolutely be plagued with defects or anomalies which can cause equipment failure before the UPS can function and provide auxiliary power to the critical load. Many non-ferroresonant power conditioners can pass the line anomalies directly to the critical load.
The instant invention does not rely on power failure to operate. Instead the continuously measured defects, as data, are stored and then are analyzed in a "Trend Analyzer", and it becomes possible to predict that the AC line, while not failed at the time of measurement, will most likely experience a predicted or imminent failure.
The use of the Ferroresonant transformer, in cooperation with the instant invention, fulfills the need for an ideal power conditioner. When coupled with an inverter module, a nearly perfect UPS is created. It is important to realize that the operation of the present invention is not dependent upon they type of power conditioner or inverter attached thereto, however, the use of the Ferroresonant transformer represents the Best Mode for the present invention. The present invention is a system for analyzing and computing the trend of potential line failures. The ferroresonant transformer is not claimed as part of the instant invention, but its use therein represents the best mode of application of the instant invention.
Unfortunately, Ferroresonant transformers are heavy, large, and costly to produce. In an attempt to produce a less costly power conditioner, attempts to eliminate the Ferroresonant transformer by using conventional linear transformers and inductors in combination with relays which switched the taps on the transformer in order to achieve a crude form of voltage regulation, were tried. These methods were only partially successful.
The conventional linear transformer, however, lacked the isolating and voltage regulation characteristic of the Ferroresonant transformer, and large voltage spikes or transients could pass through the linear transformers with very little attenuation. Slowly, despite the proven advantages of the Ferroresonant transformer, the power protection industry has moved away from the device, simply to reduce costs.
Combinations of inductors, capacitors, transformers, thyrectors, relays, and semiconductor invertors have been used in an effort to produce less expensive power protection devices which can protect sensitive power equipment such as computers, medical equipment and the like.
These less costly protection devices met with very limited success. Many contained an input relay whose operating coil was connected across the input power line. When the AC power fails, the relay will drop out, disconnecting the inverter from the line and connecting a local battery to the inverter circuit. These simple systems, often called a "Standby UPS" did not provide the type of power protection that industry and the home required. Many of these inexpensive "power protection" devices produced square waves instead of sine waves as the protected power. These square wave devices often provided their own break in the flow of power during transfer from line to battery operation, or from battery back to line. These breaks in power flow ranged from four to 22 milliseconds, and sometimes longer.
Standards were developed by The IEEE Std. 446-1995, (and others) to prescribe the minimum level of power protection that could be provided and still offer "adequate" protection. As the devices for power protection were made smaller, and cheaper, the amount of protection that they could provide also diminished. This was considered to be an acceptable alternative, but the change in direction was not very good for the end user. In general, the user who purchased one of these smaller, cheaper, power protection devices was deprived of essential protection, without his knowledge. The user was never aware of the totality of the actual AC line deficiencies. Except for the total loss of power, there was no way for him to know what was happening to the power lines, and he could not determine if his protection device was properly installed or whether the power conditioner was sufficient to protect the attached expensive equipment. The only indicator that the user had was his equipment failure, and by then it was too late.
Despite the reduction in performance, the efforts to reduce weight and cost, have resulted in simpler power protection devices. Some very simple "power protection devices" consist of only a thyrector type of energy absorber which is connected in parallel with the power line. The surge protector device is not a line power conditioner at all. Many of these power protection systems, often called "Surge Protectors", and many less expensive power conditioners as well, allow the low side of the A.C. power line, or "neutral conductor" to directly pass through from the A.C. mains to the protected load, greatly reducing the amount of protection that was actually provided.
Some of these cheaper systems allow as much as thirty to fifty volts of "pass-through" voltage to impinge upon the computer or sensitive electronic devices. This level of pass through voltage, (thirty to fifty volts), can cause a computer or medical system to fail or to be damaged, often permanently. Recognizing these serious defects, isolation transformers, DC to DC conversion, and extensive filtering have been used to minimize the problem of voltage transient pass-through on the low side of the line.
These methods of filtering have been successful, but the added cost became comparable to the cost of the Ferroresonant transformer type of line conditioner.
By re-introducing the necessity for an isolation transformer, the obvious advantage of size and weight of the smaller power conditioners has been lost. Time and technology has proven that there is no combination of devices that can duplicate the Ferroresonant transformer as a power conditioner-isolation device. One often unrecognized feature of the Ferroresonant transformer is its low bandwidth.
This important feature prevents electrical noise which may be generated within the attached equipment from passing back to the power line.
The Present Inventive Entity
Many line conditioners and power conditioners have been developed to protect critical equipment from power line disturbances. These devices, upon recognizing the existence of a major fault on the AC lines immediately revert to inverter operation.
Many of these devices perform very effectively, providing a flow of continuous uninterrupted power to the critical load. One major problem still exists, a debilitating fault must occur before the system is operable.
The point of novelty of the present invention is the ability to recognize AC line faults, both small and large, measure am and quantify them, store the data, and analyze the measured results for type of disturbance, repetition, frequency, amplitude, and duration. Trend analysis circuitry and software stores the accumulated failure data and computes the potential for failure, alerting the user that, where necessary, an inverter module is required to permanently solve the line power problems that have been encountered. A complete log of the measured defects, their duration, date and time is printed out for the user, and the data can also be seen on a connected video display. The invention described herein can also be applied to DC (Direct Current) power systems.
Another unique feature of the present invention is that in many cases, an inverter module is not required because the defects seen on the lines are trivial, and well within the capability of the Ferroresonant transformer or other type of power conditioner to provide the required power protection. It is only when the trend analysis reveals that conditions continuously or repeatedly exist on the power lines which can lead to failure, that an inverter module should be used.
The major element and novelty of the present invention is a software control process which determines the overall protective operation of the new power conditioner.
Note that the terminology "line conditioner" and "power conditioner" as used herein are synonymous. Both terms are used equally in the power protection industry.
Under software control, the present invention measures and detects the following line deficiencies:
A) Line transients: Peak pulse amplitude and pulse width, time of day, and duration are measured. The system accumulates data and then analyses the trend of the transients. If the trend indicates a potential line failure, an inverter should be attached, an alarm is sounded. Alarms can be visual or audible, and a voice module advises the user that the connection of an inverter module is suggested. If an inverter is attached, the system will automatically revert to inverter operation.
B) Line voltage glitches are measured within each cycle of input voltage and detected and counted. An allowable number of glitches is entered as a "glitch count" (N). At the glitch count number that has been entered, minus 1 (N-1), an alarm is sounded indicating that there are a dangerous number of glitches occurring on the power mains. At the preset number of glitches (N), the system reverts to inverter operation. If no inverter is attached, the system sounds an alarm at (N-1 glitches), advising the user that an inverter is necessary. In addition, the system counts glitches per timing interval, and analyzes the trend of the glitches that are occurring. If the glitch count is rising, an alarm is sounded indicating that the trend depicts imminent line failure. During normal operation, glitches are counted within a line cycle. (16.6 milliseconds at 60 Hz), but the invention allows the glitch count period or interval to be seconds, minutes, hours, days, weeks, or months, as desired. The variable timing interval is a wonderful diagnostic tool. Of course, as the time is extended, the number of glitch counts is increased accordingly.
At three glitch counts per cycle, the same limits are computed to be:
______________________________________ Per cycle 3 Per second 180 Per minute 4800 Per hour 288,000 ______________________________________
It is not expected that long duration glitch counts will be tolerated, and glitch counts are generally measured during a single cycle or on a per second basis to predict the potential for failure. Other defects such as transients, line voltage excursions, noise, dropouts, can be measured and stored over the specified intervals.
C) Surges and sags of incoming line voltage are measured and data is stored. The system must provide constant voltage to the attached load. Under software control, the system measures all surges and sags of the input voltage. Data is stored and analyzed. The trend is analyzed and the user is alerted when the trend predicts possible line failure, or potential damage to attached equipment.
D) Incoming line frequency is measured. Upper and Lower acceptable limits of frequency are pre-programmed by the operator or under software control. This is an important feature which is overlooked on simple, less-expensive power protection systems. When the power protection device is used with an automatic gasoline generator, diesel generator, or a wind or water powered electrical system, measurement of incoming frequency is of great importance. When the out-of-frequency detector determines that
the incoming frequency is out of limits or is apt to go out of the specified limits, PA1 the system reverts to inverter operation. Appropriate alarms and readouts are activated. PA1 Store data Voltage magnitude, date, time, duration, frequency of changes. PA1 If line voltage is greater than upper limit, go to inverter. PA1 If line voltage is less than lower limit, go to inverter. PA1 If line voltage is within range, monitor power conditioner output PA1 Store input line voltage, output voltage, analyze data develop control feedback. PA1 for regulation. Store all data. PA1 If glitch count per cycle or test interval exceeds limit set (usually three during a line cycle), alert the user, and then transfer alarm data into the Log Buffer. PA1 If an Inverter is attached, initiate inverter. PA1 If glitch count approaches but does not exceed the lower limit, (usually 2), alert user that an inverter may be needed. No Inverter attached? Do not Initiate inverter. PA1 Initiating inverter automatically disconnects the incoming AC line. PA1 Does the trend analyzer indicate that there are excessive transients, and the rate of increase is increasing, then initiate Inverter required alarm. PA1 Inverter attached? Initiate inverter PA1 Store data--Inverter control, to Log Buffer for printout or display. PA1 Analyze input voltage history, Store data, date and time, PA1 Trend: is Input voltage falling? PA1 If trend reveals that voltage is crawling toward upper or lower limits, advise, sound alarms alert the user that inverter an inverter is needed. Transfer all data to the Log Buffer for digital printout or Video display. PA1 Examine all stored data. PA1 Trend: Average dropouts increasing? PA1 Trend: Average dropout interval increasing? PA1 Trend: Average dropouts decreasing? PA1 Trend: average dropout interval decreasing? PA1 If trend reveals that dropouts are increasing alert user that an inverter will be required. Some power conditioners supplement line power during disturbances by providing interactive power during a short power failure. PA1 Store data: are the number of transients per interval increasing? PA1 Are the number of transients per interval decreasing? PA1 Is the Transient amplitude increasing? PA1 Is the Transient interval decreasing? PA1 Perform the Trend Analysis. PA1 If transient amplitude is increasing, or the transient repetition rate is increasing, advise the user that a problem exists. The use of an inverter may not be necessary. PA1 A) Digital printout of detected failures which had been entered into the Log Buffer. PA1 B) CRT (video monitor) readout of detected failures, which had been entered into the Log Buffer. PA1 C) Provide Audio (Speech Dialog) of the identified problem areas when the trend analyzer reveals potential for power line failure. Normal failures are revealed by audible and visual alarms. PA1 Hourly, daily, weekly or monthly. Standard is Daily. In addition, Weekly, Monthly, are user selectable. PA1 Diagnostic: Hourly, minute, second, or cyclic. This function disables the Standard intervals.
Inverter operation provides a frequency which is more accurate and stable than the power lines from the power company. Precise frequency to the critical load is therefore guaranteed.
Fortunately, most power disturbances persist for extremely short durations. If these transients are allowed to appear in the attached electronic equipment, they can and do produce stresses on the electrical circuits. These disturbances and induced stresses may not cause instant failure. They can initiate a process which can result in early failure of the attached equipment. These failures can prove to be extremely costly. If there was a way of knowing the extent and duration of line transients and voltage excursions, the expected lifetime, or prediction of future failure can be accurately determined.
The software of the present invention satisfies the requirement for failure prediction through a process of trend analysis of all measured line defects.
With today's expensive and sophisticated equipment, it is no longer adequate to simply protect the critical load from line voltage anomalies at the instant that they occur. Prediction of possible line failure, and of expected life service become of paramount importance. The ability to predict potential or real failure of a computer controlled system may be more valuable than the cost of the protection equipment. The most novel feature of the present invention is the use of microprocessors and computer technology to measure the AC power line defects which are described above, and to analyze the duration and frequency of these events. The software then analyzes the occurrences, integrating them over time. The software process also predicts whether the line is experiencing an excessive number of defects, and whether the measured defects are increasing or decreasing with time. The trend analyzer then alerts the operator that he is apt to have a failure due to the measured defective characteristics, and suggests the addition of an inverter and battery system, if required. The software can also control the Ferroresonant transformer regulation, improving its overall operating efficiency, and reducing its' output impedance.
The software also can provide the user with a complete printed record of the AC line conditions in his home or factory installation, improving the ability to diagnose power faults and correct them. Line transients, dropouts, surges, sags, electrical noise, incoming frequency, and short term outages are recorded automatically. The measured defects, the quantity and the time and date are provided to the user in an operating log format. The logged data is stored in a buffer which can be downloaded to a digital printer or a video display upon demand or at a pre-programmed time. The reporting interval and format is selectable by the user as per cycle, per second, per minute, hourly, daily, weekly, or monthly.
Where the line sag exceeds the capability of the controlled Ferroresonant transformer, or other power protection device, to provide active compensation, and to provide power during a break in the input, or where other line defects exist, the user is alerted and measured data is transferred into the Log Buffer. Where conditions of power quality are extremely bad, the system can inhibit the attached electrical equipment operation. The user will then have the option of adding a plug-in battery and inverter option which converts the line conditioner of the instant invention into a true no-break Uninterruptible Power Supply. (UPS)
It is well documented that more than 95% of power outages are of very short duration. These outages last for four milliseconds or less. With a properly designed Ferroresonant power conditioner, the battery backup (Inverter) option often becomes unnecessary, and the inclusion of the battery backup option becomes an unnecessary expense. The battery backup option should be used only when the application calls for it. Non-Ferroresonant power conditioners often employ large capacitor banks to provide the necessary "ride through", so that inserters are not necessary for short transient outages.
When an inverter is connected, the power conditioner will provide battery charging and battery management. The present invention keeps track of outages, totalizes them, and advises the user when to add the battery backup or inverter option. This option is often called a UPS option. The same trend analysis circuits and logs can be configured to keep track of battery drain and be used to control the battery charger in order to maintain optimum battery life.
The present invention allows the inverter option (or UPS) to be an independent entity, and one which can be attached by means of a simple plug-in assembly. By adding this option only when necessary, this invention saves on the additional cost, and the UPS function will be utilized only when needed. In many cases, a battery backup UPS has proven not to be necessary. The improved voltage regulation, isolation, transient protection, and power carry-through, provided by a properly designed Ferroresonant transformer, is all the protection that is needed. It is important to note that when a non-ferroresonant power conditioner is used, a type which is not able to "ride through" a 20 millisecond outage, the battery backup option becomes essential.
In addition to improved power conditioning, and data collection and reporting, this invention defines and fulfills the need for accurate data collection, improved power management, improved efficiency and economy, and power line defect trend analysis. The algorithm of the instant invention solves many of the heretofore known problems associated with the Ferroresonant transformer and other battery powered inverter type line conditioners. Operating efficiency is increased, size and weight are reduced, and initial installation cost is reduced, and interconnectivity or paralleling of Ferroresonant transformers without excessive circulating currents has been achieved.